First of all: request doesn't mean emergency, you take your time of course, I just confine myself to pointing out flaws and improvements, then you make your choice and eventually, implement those changes when you deem it fit.

It's not in Unicode tables because Arabic Presentation Forms were designed for strictly Arabic usage, they don't contain non-Arab letter, and JEH is indeed a Turkish, that is non-Arab letter, so that's why you won't find it in there but you'll find REH and ZAIN, which are Arabic letters. But Arabic Presentation Forms were obsolete by the time the Unicode Consortium implemented non-Arab letters, so they didn't bother adding new ligatures.

About the evidence: I don't mind ligatures, but if you want to implement that type of ligature, you should include all REH-looking letters, not just REH & ZAIN. There are two things you need to understand about Arabic and every typographer will confirm what I'm about to say:

1. To understand the Arabic script, you need to deal with letter shapes, not letters "tout court", like in Latin, Cyrillic and Greek, because it's the letter shape which tells you the contextual forms, that is the peculiar shape the letter is going to assume according to the position it occupies in the word.

2. Ligatures in Arabic are functionally just customised, "cool", powered-up contextual forms and therefore they must adopt the same adamant logic as basic contextual forms.

Regarding jeh: I was waiting for your response to my comment of 07.09. I think I provided there the best explanation I could.

Can you give me some clue as to why this presentation form isn't in the Unicode tables? Is it of secondary importance to the zain? or is it used in some other kind of text as the zain?

Please understand I have limited resources here, while I'm being asked to do several other things at the same time as you make your requests. It really helps me if you can provide some kind of outside evidence substantiating a request.

Now the ligature works for ZAIN but you haven't implemented it for JEH yet. Why? As I said, the shape is the same and seeing ZAIN in ligature and JEH not, it jumps out at you, and, believe me, it's not pretty at all, actually very sloppy. If you take a look at the Unicode table, there are other nine letters (besides JEH), which share the same letter shape as ZAIN and REH.